I believe I’ve seen it on some Heroku buildpacks for static content. It will make it easy for people to setup their static sites on Glitch without messing with package.json and server.js and learning a lot of details about NPM, Node.js, serving requests etc.
It’s not the cleanest solution and doesn’t account for the Strict-Transport-Security you’ve specified in your static.json though so it may not work for this particular project…but, if anyone else is experiencing a similar issue and wants to use Glitch the fastest workaround without having to completely delete package.json would be to update the start script in package.json.